1. Field of the Invention
The present invention relates to a technique for regenerating a secondary battery at a low temperature, particularly to a technique for improving the power performance of a vehicle such as a pure electric vehicle or a hybrid electric vehicle during start-up and during driving in an environment of a low temperature by controlling the charge and discharge of the secondary battery.
2. Related Background Art
Examples of the secondary battery include lead batteries, nickel-cadmium (Ni-Cd) batteries, nickel-metal-hydride (Ni-MH) batteries, and lithium ion batteries, etc. Such batteries have a characteristic in that they are connected to an external power source and thereby they can be charged with a predetermined current applied from the power source when their electric power is consumed. These batteries conventionally have been used for various equipment, using such a characteristic.
For example, such a battery is mounted on a vehicle and functions as a battery for starting an engine that supplies electric power to an ignition plug of its engine during start-up. Recently, Ni-MH battery is used also as a main power source for driving a pure electric vehicle or a so-called hybrid electric vehicle provided with an engine and the electric motor.
In the hybrid electric vehicle, when the output from the engine is larger than the power necessary for driving, the secondary battery is charged by driving an electric generator, making use of the excess power. On the contrary, when the output from an engine is smaller, the electric motor is driven by the use of the power of the secondary battery so as to supply the shortage of power. In this case, discharging of the secondary battery is carried out. When the secondary battery is mounted on the hybrid electric vehicle the vehicle is required to maintain the secondary battery in an appropriate operation condition by controlling the charge and discharge of the second battery.
Therefore, the state of charge (SOC) of the battery is estimated by detecting the voltage, current, temperature, etc., of the battery, and the SOC is controlled so that the fuel consumption efficiency becomes the best. Furthermore, in order to operate the power assist driven by the electric motor during acceleration and energy collection (regenerative braking) during deceleration with a good balance, the SOC level at this time is set to be, for example, approximately 50 to 60% as the center of control. When the SOC becomes lower than the center, this battery is controlled to be charged excessively, and on the contrary, when the SOC is higher than the center, the battery is controlled to be discharged excessively so as to bring the SOC to the center of control.
In general, when the secondary battery is at a low temperature, as compared with an ordinary operating temperature, the activation level within the battery is thought to be lowered. When the output is the same, the voltage of the secondary battery is greatly lowered. Therefore, the output duration is also shorter, thus remarkably reducing the electric power taken from the battery. On the contrary, when the charge is carried out when the battery temperature is low, since the battery voltage is increased greatly, overvoltage occurs at the side of the electric motor system, making a long-time charging impossible.
When the secondary battery is used as a power source to start the engine when the battery temperature is low, at which time the battery performance remarkably is deteriorated, the lowering of the battery voltage is increased. Therefore, every time a driver turns on a starter, the battery voltage is suddenly lowered, making it difficult to start the engine.
Furthermore, when driving a vehicle when the battery temperature is low, input/output of the battery becomes small, and sufficient power assist during acceleration and the energy collection during deceleration are impossible. Thus, under such circumstances, as a state in which the battery temperature is low lasts for a long time, energy collection efficiency is lowered due to the reduction of battery input. That is, deterioration of fuel efficiency, as well as deterioration of motor performance such as acceleration force, and ability to climb a slope, of a vehicle due to shortage of battery output may occur and serious problems such as stopping on the road may occur.
With the foregoing in mind, it is an object of the present invention to provide a device and method for controlling charge and discharge, which can exhibit the battery performance achieving its intended level of a battery by quickly raising the temperature of the battery or increasing the battery voltage by regenerating the battery when it is at a low temperature and can start the engine quickly at a low temperature.
In order to achieve the above-mentioned object, a first input/output control device of a secondary battery according to the present invention includes: a battery pack in which a plurality of cells that are secondary batteries are combined with each other; a voltage detector for detecting an output voltage of the battery pack; a current detector for detecting a charge/discharge current of the battery pack; a temperature detector for detecting the temperature within the battery pack; a state-of-charge operator for calculating the state of charge of the battery pack based on a voltage signal from the voltage detector, a current signal from the current detector, and a temperature signal from the temperature detector; a temperature rise controller for determining a central value of the state-of-charge control in the range of the state-of-charge control of the battery pack in order to control the temperature rise of the battery pack based on the temperature signal, and then outputting the central value of the state-of-charge control; and a battery input/output controller for voluntarily controlling the state of charge of the battery pack based on the central value of the state-of-charge control from the temperature rise controller and the state of charge at the point of time from the state-of-charge operator, and for controlling the charge and discharge of the battery pack based on charge and discharge requests from the outside to the battery pack.
It is preferable in the first input/output control device that when a temperature indicated by the temperature signal is lower than a predetermined temperature, the temperature rise controller allows the central value of the state-of-charge control to shift toward an upper region in the range of the state-of-charge control in corresponding to the temperature indicated by the temperature signal.
Furthermore, it is preferable in the first input/output control device that the battery input/output controller carries out a short-time charging of the battery pack after the discharge request from the outside to the battery pack is canceled.
Alternatively, it is preferable in the first input/output control device that the battery input/output controller carries out a short-time charging of the battery pack if a voltage value indicated by the voltage signal from the voltage detector becomes lower than a predetermined voltage when the output control of the battery pack is carried out based on the discharge request from the outside to the battery pack.
In order to achieve the above-mentioned object, a second input/output control device of the secondary battery according to the present invention includes: a battery pack being mounted on a vehicle provided with an electric motor and an electric generator, in which the electric motor is used as a driving source; the battery pack including a plurality of cells that are secondary batteries combined with each other and having positive and negative poles connected to the vehicle; a voltage detector for detecting an output voltage of the battery pack; a current detector for detecting a charge/discharge current of the battery pack; a temperature detector for detecting the temperature within the battery pack; a state-of-charge operator for calculating the state of charge of the battery pack based on a voltage signal from the voltage detector, a current signal from the current detector, and a temperature signal from the temperature detector; a temperature rise controller for determining a central value of the state-of-charge control in a range of the state-of-charge control of the battery pack in order to control the temperature rise of the battery pack based on the temperature signal, and then outputting the central value of the state-of-charge control; and a battery input/output controller for voluntarily controlling the state of charge of the battery pack based on the central value of the state-of-charge control from the temperature rise controller and the state of charge at the point of time from the state-of-charge operator, and for controlling the charge and discharge of the battery pack based on charge and discharge requests commanded by a driver to the battery pack.
It is preferable in the second input/output control device that when a temperature indicated by the temperature signal is lower than a predetermined temperature, the temperature rise controller allows the central value of the state-of-charge control to shift toward an upper region in the range of the state-of-charge control in corresponding to the temperature indicated by the temperature signal.
Furthermore, it is preferable in the second input/output control device that the battery input/output controller carries out a short-time charging of the battery pack after the discharge request commanded by the driver to the battery pack is canceled.
Alternatively, it is preferable that the battery input/output controller carries out a short-time charging of the battery pack if the voltage value indicated by the voltage signal from the voltage detector becomes lower than a predetermined voltage when the output control of the battery pack is carried out based on the discharge request commanded by the driver to the battery pack.
In order to achieve the above-mentioned object, an input/output control method of the secondary battery according to the present invention includes: detecting an output voltage, a charge/discharge current, and a temperature of a battery pack in which a plurality of cells that are secondary batteries are combined with each other; calculating a state of charge of the battery pack based on the detected output voltage, charge/discharge current and temperature; setting a central value of the state-of-charge control in a range of the state-of-charge control in an upper region in the range of the state-of-charge control when the detected temperature becomes lower than a predetermined temperature; determining a difference between the calculated state of charge and the set central value of the state-of-charge control, and carrying out the charging of the battery pack based on the difference to control the temperature rise of the battery pack.
It is preferable in the input/output control method of the secondary battery that a short-time charging of the battery pack is carried out after a discharge request to the battery pack is canceled.
Alternatively, it is preferable that a short-time charging of the battery pack is carried out if the detected output voltage becomes lower than a predetermined voltage when discharging of the battery pack is carried out based on a discharge request to the battery pack.
In order to achieve the above-mentioned object, a third input/output control device of a secondary battery according to the present invention includes: a battery pack being mounted on a vehicle provided with an electric motor and an electric generator, in which the electric motor or an engine is used as a driving source, the battery pack including a plurality of cells that are secondary batteries combined with each other and having positive and negative poles connected to the vehicle; a voltage detector for detecting an output voltage of the battery pack; a current detector for detecting a charge/discharge current of the battery pack; a temperature detector for detecting the temperature within the battery pack; a rotational speed detector for detecting the rotational speed of the engine, and a battery input/output controller for judging whether the start-up of the engine fails based on a voltage signal from the voltage detector, a current signal from the current detector, a temperature signal from the temperature detector, and a rotational speed signal from the rotational speed detector.
It is preferable in the third input/output control device that the battery pack is used as a power source to start the start-up of the engine when an output of a start-up command from a driver is issued, and the start-up of the engine is stopped when the voltage value indicated by the voltage signal from the voltage detector of the battery pack becomes lower than a predetermined value, or the rotational speed signal from the rotational speed detector becomes lower than a predetermined rotational speed.
Furthermore, it is preferable in the third input/output control device that after the start-up of the engine is stopped, the battery input/output controller carries out a short-time charging of the battery pack by means of an external charger or the like, and thereafter carrying out a start-up of the engine again.
Furthermore, it is preferable in the third input/output control device that after the start-up of the engine is stopped, the battery input/output controller carries out a regeneration with respect to the battery pack by the revolving of the engine, and thereafter carrying out a start-up of the engine again.
According to the above-mentioned configuration and method, when the battery temperature is low, by setting a central value of the state-of-charge (SOC) control to the upper region in a range of the control by means of software, the frequency of charging in the region in which the charging efficiency is deteriorated becomes higher, so that the reaction heat by charging can increase the battery temperature quickly, thus making the most of the battery performance. Consequently, serious problems such as the deterioration of a motor performance of a vehicle, stopping on the road, etc. can be avoided, thus improving the marketability as a vehicle. Furthermore, since software control can be employed, no hardware is added, and thus, the cost of the device is not increased.
Furthermore, a control is carried out so that a short-time charging is carried out after the battery discharge request is cancelled, since the battery voltage, which was lowered by discharging, can be increased quickly, the subsequent battery output performance can be improved, thus also making it possible to enhance the marketability as a vehicle.
Furthermore, in a vehicle using a secondary battery for start-up of the engine as a power source, by carrying out a short-time charging when the engine is started up at a low temperature, after a battery discharge is carried out by the operation of a starter and the discharge is stopped because it is judged that the start-up of the engine is difficult by the battery input/output controller, the battery voltage can be increased. At the same time, since the crank shaft of engine is revolved by a first operation of the starter, it is possible to lower the viscosity of engine oil, thus making it possible to start up the vehicle at a low temperature the second time or later by the inertial revolution of the crankshaft.